Clayware such as porcelain, bone china, earthenware, the so-called ironstones, aluminous ceramics, hotel wares and ceramic tiles, is produced by firing a composition containing clay and flux.
Fluxes conventionally used in making clayware, such as exemplified above, are feldspars, nepheline syenite and Cornish stone. U.S. Pat. No. 3,704,146 describes fluxes for "white-ware" ceramic compositions comprising clay, flint and a flux, the fluxes being ground vitreous frits which may contain up to about 45% by weight of boric oxide. U.S. Pat. No. 4,219,360 describes use of B.sub.2 O.sub.3 containing frits in manufacturing bone china. However, a frit is expensive to produce because of the energy consumption, the need for refractory furnace linings and because of the need to grind the product. Furthermore, the frits have been found not to be suitable for some clayware compositions due to slight leaching of boric oxide from the frit during manufacture of ceramic articles, for example, in preparing casting slips. U.S. Pat. Nos. 3,303,036 and 3,532,522 also describe use of inorganic borates in manufacturing ceramic ware.
Zeolites have been proposed as components of ceramic compositions especially in the production of lightweight ceramics. See, for example, Japanese Patent Nos. 69 23,815-7 and Japanese Patent Application No. 73 39,513. However, none of the zeolites are known to contain boron and the zeolites are used to confer refractory properties on the ceramics and are not used as fluxes.